1. Field of the Invention
This invention relates to various improvements for prosthetic valves, including but not limited to transcatheter mitral valve replacement prosthetics and delivery devices therefor.
2. Background of the Invention
The current state of knowledge is as follows.
Valvular heart disease and specifically aortic and mitral valve disease is a significant health issue in the US. Annually approximately 90,000 valve replacements are conducted in the US. Traditional valve replacement surgery, the orthotopic replacement of a heart valve, is an “open heart” surgical procedure. Briefly, the procedure necessitates surgical opening of the thorax, the initiation of extra-corporeal circulation with a heart-lung machine, stopping and opening the heart, excision and replacement of the diseased valve, and re-starting of the heart. While valve replacement surgery typically carries a 1-4% mortality risk in otherwise healthy persons, a significantly higher morbidity is associated to the procedure largely due to the necessity for extra-corporeal circulation. Further, open heart surgery is often poorly tolerated in elderly patients.
Thus, if the extra-corporeal component of the procedure could be eliminated, morbidities and the costs of valve replacement therapies would be significantly reduced.
While replacement of the aortic valve in a transcatheter manner has been the subject of intense investigation, lesser attention has been focused on the mitral valve. This is in part reflective of the greater level of complexity associated to the native mitral valve apparatus and thus a greater level of difficulty with regards to inserting and anchoring the replacement prosthesis.
Several designs for catheter-deployed (transcatheter) aortic valve replacement are under various stages of development. The Edwards SAPIEN transcatheter heart valve is currently undergoing clinical trial in patients with calcific aortic valve disease who are considered high-risk for conventional open-heart valve surgery. This valve is deployable via a retrograde transarterial (transfemoral) approach or an antegrade transapical (transventricular) approach. A key aspect of the Edwards SAPIEN and other transcatheter aortic valve replacement designs is their dependence on lateral fixation (e.g. tines) that engages the valve tissues as the primary anchoring mechanism. Such a design basically relies on circumferential friction around the valve housing or stent to prevent dislodgement during the cardiac cycle. This anchoring mechanism is facilitated by, and may somewhat depend on, a calcified aortic valve annulus. This design also requires that the valve housing or stent have a certain degree of rigidity.
At least one transcatheter mitral valve design is currently in development. The Endovalve uses a folding tripod-like design that delivers a tri-leaflet bioprosthetic valve. It is designed to be deployed from a minimally invasive transatrial approach, and could eventually be adapted to a transvenous atrial septotomy delivery. This design uses “proprietary gripping features” designed to engage the valve annulus and leaflets tissues. Thus the anchoring mechanism of this device is essentially equivalent to that used by transcatheter aortic valve replacement designs.
One problem involves the repetitive deformation of the nitinol wire material commonly used in the manufacture of stented valves. Fatigue fractures of the metal wire material can result in a catastrophic structural failure whereby the valve support structure weakens and breaks. Although failure of a single wire may not necessarily cause a structural collapse of the entire valve, over time, this possibility becomes a practical reality. When the consequence of valve failure means the death of the patient, the importance cannot be overstated.
Various problems continue to exist in this field, including problems with perivalvular leaking around installed prosthetic valve, lack of a good fit and stability for the prosthetic valve within the native mitral annulus, atrial tissue erosion, excess wear on the metallic structures, interference with the aorta at the posterior side of the mitral annulus, difficulties in deployment and retrieval, and lack of customization, to name a few. Accordingly, there exists a need for the improvement inventions disclosed herein.